A nozzle clamping nut holds the two main components of the fuel injector—an injection nozzle and a valve body—tightly together. When the fuel injector is mounted to the cylinder head, the injection nozzle protrudes into a combustion chamber of a motor vehicle engine, the valve body disposed thereabove actuating the injection nozzle. It is necessary here to seal off the fuel injector from the combustion chamber at the cylinder head. This is accomplished by appropriate design of the nozzle clamping nut acting in conjunction with a corresponding device, a seal seat, in the cylinder head.
Such a sealing arrangement must meet exacting requirements. On the one hand, the sealing arrangement is exposed to high thermal loads (−40° C. for cold starting in winter, to over +150° C.) during operating conditions and, on the other hand, the sealing device is subject to high mechanical stress, particularly vibration loads. In addition, the sealing arrangement must ensure a durable, long-lasting seal between fuel injector and cylinder head.
In the prior art there is embodied for this purpose, e.g. on the nozzle clamping nut, a horizontal rim which is seated on a likewise horizontal rim provided in the injector bore, and the nozzle clamping nut or rather the fuel injector is pressed with high static force against the cylinder head. By providing a large areal overlap of the two rims, it is intended to create a durable fluid-tight joint.
The injector is generally sealed off from the combustion chamber by a metal sealing washer. This sealing is necessary because of the hot exhaust gases and the pressure loss in the cylinder. Due to the high combustion temperatures and high cylinder pressures, sealing is only possible using a metal sealing washer, so that no combustion gases can flow directly past the injector and into the environment.
In DE 101 02192 A1, a nozzle clamping nut has, on a free end, a truncated cone shaped region which can be inserted in a corresponding truncated cone shaped injector bore section. In the preassembled state, i.e. when the fuel injector with nozzle clamping nut is inserted in the truncated cone shaped injector bore, there is a circumferential angular difference of 2° to max. 5° between the truncated cone on the nozzle clamping nut and the truncated cone bore in the cylinder head. This ensures that the fuel injector is centered in the injector bore, the fuel injector then being pressed with high static force into the bore and a common sealing surface being formed between the truncated cone of the nozzle clamping nut and conical arc in the cylinder head.
Mixture and the hot combustion gases flow as far as the sealing locations of nozzle clamping nut and nozzle body, and also the seal between injector and cylinder head. In this gap there is now a build-up of unburned mixture and exhaust gases, e.g. H2O and S. After the engine is turned off, condensation of electrolyte (water) may now occur in the cool-down phase. The electrolyte promotes ion exchange and therefore corrosion.
In the prior art it is also known to screw the nozzle tightly to the nozzle clamping nut without any additional sealing. Also known is protecting the nozzle body from heat by coating it and installing sleeves as heat sinks. However, new combustion methods appear to cause corrosion precisely in this area, so that direct sealing against corrosive substances from combustion gases is absolutely necessary in this region.